ElectromagnetismElectromagnetismElectromagnetism is a branch of physics involving the study of the
electromagnetic force, a type of physical interaction that occurs
between electrically charged particles. The electromagnetic force
usually exhibits electromagnetic fields such as electric fields,
magnetic fields and light, and is one of the four fundamental
interactions (commonly called forces) in nature. The other three
fundamental interactions are the strong interaction, the weak
interaction and gravitation.[1]
LightningLightning is an electrostatic discharge that travels between two
charged regions.The word electromagnetism is a compound form of two Greek terms,
ἤλεκτρον ēlektron, "amber", and μαγνῆτις λίθος
magnētis lithos,[2] which means "Μagnesian stone",[3] a type of iron
ore
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Electric Potential
An electric potential (also called the electric field potential,
potential drop or the electrostatic potential) is the amount of work
needed to move a unit positive charge from a reference point to a
specific point inside the field without producing any acceleration.
Typically, the reference point is Earth or a point at Infinity,
although any point beyond the influence of the electric field charge
can be used.
According to classical electrostatics, electric potential is a scalar
quantity denoted by V, equal to the electric potential energy of any
charged particle at any location (measured in joules) divided by the
charge of that particle (measured in coulombs). By dividing out the
charge on the particle a quotient is obtained that is a property of
the electric field itself.
This value can be calculated in either a static (time-invariant) or a
dynamic (varying with time) electric field at a specific time in units
of joules per coulomb (J C−1), or volts (V)
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Electrical Network
An electrical network is an interconnection of electrical components
(e.g. batteries, resistors, inductors, capacitors, switches) or a
model of such an interconnection, consisting of electrical elements
(e.g. voltage sources, current sources, resistances, inductances,
capacitances). An electrical circuit is a network consisting of a
closed loop, giving a return path for the current. Linear electrical
networks, a special type consisting only of sources (voltage or
current), linear lumped elements (resistors, capacitors, inductors),
and linear distributed elements (transmission lines), have the
property that signals are linearly superimposable. They are thus more
easily analyzed, using powerful frequency domain methods such as
Laplace transforms, to determine DC response, AC response, and
transient response.
A resistive circuit is a circuit containing only resistors and ideal
current and voltage sources
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Eddy CurrentEddy currentsEddy currents (also called Foucault currents) are loops of electrical
current induced within conductors by a changing magnetic field in the
conductor due to Faraday's law of induction.
Eddy currentsEddy currents flow in
closed loops within conductors, in planes perpendicular to the
magnetic field. They can be induced within nearby stationary
conductors by a time-varying magnetic field created by an AC
electromagnet or transformer, for example, or by relative motion
between a magnet and a nearby conductor. The magnitude of the current
in a given loop is proportional to the strength of the magnetic field,
the area of the loop, and the rate of change of flux, and inversely
proportional to the resistivity of the material.
By Lenz's law, an eddy current creates a magnetic field that opposes
the change in the magnetic field that created it, and thus eddy
currents react back on the source of the magnetic field
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Electromagnetic Pulse
An electromagnetic pulse (EMP), also sometimes called a transient
electromagnetic disturbance, is a short burst of electromagnetic
energy. Such a pulse's origination may be a natural occurrence or
man-made and can occur as a radiated, electric, or magnetic field or a
conducted electric current, depending on the source.
EMP interference is generally disruptive or damaging to electronic
equipment, and at higher energy levels a powerful EMP event such as a
lightning strike can damage physical objects such as buildings and
aircraft structures
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Ohm's LawOhm's lawOhm's law states that the current through a conductor between two
points is directly proportional to the voltage across the two points.
Introducing the constant of proportionality, the resistance,[1] one
arrives at the usual mathematical equation that describes this
relationship:[2] I
= V
R , displaystyle I= frac V R , where I is the current through the conductor in units of amperes, V is
the voltage measured across the conductor in units of volts, and R is
the resistance of the conductor in units of ohms. More specifically,
Ohm's lawOhm's law states that the R in this relation is constant, independent
of the current.[3]
The law was named after the German physicist Georg Ohm, who, in a
treatise published in 1827, described measurements of applied voltage
and current through simple electrical circuits containing various
lengths of wire
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Static ElectricityStatic electricityStatic electricity is an imbalance of electric charges within or on
the surface of a material. The charge remains until it is able to move
away by means of an electric current or electrical discharge. Static
electricity is named in contrast with current electricity, which flows
through wires or other conductors and transmits energy.[1]
A static electric charge can be created whenever two surfaces contact
and separate, and at least one of the surfaces has a high resistance
to electric current (and is therefore an electrical insulator). The
effects of static electricity are familiar to most people because
people can feel, hear, and even see the spark as the excess charge is
neutralized when brought close to a large electrical conductor (for
example, a path to ground), or a region with an excess charge of the
opposite polarity (positive or negative)
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Insulator (electricity)
An electrical insulator is a material whose internal electric charges
do not flow freely; very little electric current will flow through it
under the influence of an electric field. This contrasts with other
materials, semiconductors and conductors, which conduct electric
current more easily. The property that distinguishes an insulator is
its resistivity; insulators have higher resistivity than
semiconductors or conductors.
A perfect insulator does not exist, because even insulators contain
small numbers of mobile charges (charge carriers) which can carry
current. In addition, all insulators become electrically conductive
when a sufficiently large voltage is applied that the electric field
tears electrons away from the atoms. This is known as the breakdown
voltage of an insulator. Some materials such as glass, paper and
Teflon, which have high resistivity, are very good electrical
insulators
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Direct CurrentDirect currentDirect current (DC) is the unidirectional flow of electric charge. A
battery is a good example of a DC power supply.
Direct currentDirect current may
flow in a conductor such as a wire, but can also flow through
semiconductors, insulators, or even through a vacuum as in electron or
ion beams. The electric current flows in a constant direction,
distinguishing it from alternating current (AC). A term formerly used
for this type of current was galvanic current.[1]
The abbreviations AC and DC are often used to mean simply alternating
and direct, as when they modify current or voltage.[2][3]
Direct currentDirect current may be obtained from an alternating current supply by
use of a rectifier, which contains electronic elements (usually) or
electromechanical elements (historically) that allow current to flow
only in one direction
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MagnetostaticsMagnetostaticsMagnetostatics is the study of magnetic fields in systems where the
currents are steady (not changing with time). It is the magnetic
analogue of electrostatics, where the charges are stationary. The
magnetization need not be static; the equations of magnetostatics can
be used to predict fast magnetic switching events that occur on time
scales of nanoseconds or less.[1]
MagnetostaticsMagnetostatics is even a good
approximation when the currents are not static — as long as the
currents do not alternate rapidly.
MagnetostaticsMagnetostatics is widely used in
applications of micromagnetics such as models of magnetic recording
devices
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Magnetic Potential
The term magnetic potential can be used for either of two quantities
in classical electromagnetism: the magnetic vector potential, A,
(often simply called the vector potential) and the magnetic scalar
potential, ψ. Both quantities can be used in certain circumstances to
calculate the magnetic field.
The more frequently used magnetic vector potential, A, is defined such
that the curl of A is the magnetic field B. Together with the electric
potential, the magnetic vector potential can be used to specify the
electric field, E as well. Therefore, many equations of
electromagnetism can be written either in terms of the E and B, or in
terms of the magnetic vector potential and electric potential
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Gauss's Law For Magnetism
In physics,
Gauss's lawGauss's law for magnetism is one of the four Maxwell's
equations that underlie classical electrodynamics. It states that the
magnetic field B has divergence equal to zero,[1] in other words, that
it is a solenoidal vector field. It is equivalent to the statement
that magnetic monopoles do not exist.[2] Rather than "magnetic
charges", the basic entity for magnetism is the magnetic dipole. (If
monopoles were ever found, the law would have to be modified, as
elaborated below.)
Gauss's lawGauss's law for magnetism can be written in two forms, a differential
form and an integral form. These forms are equivalent due to the
divergence theorem.
The name "
Gauss's lawGauss's law for magnetism"[1] is not universally used
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Magnetization
In classical electromagnetism, magnetization or magnetic polarization
is the vector field that expresses the density of permanent or induced
magnetic dipole moments in a magnetic material. The origin of the
magnetic moments responsible for magnetization can be either
microscopic electric currents resulting from the motion of electrons
in atoms, or the spin of the electrons or the nuclei. Net
magnetization results from the response of a material to an external
magnetic field, together with any unbalanced magnetic dipole moments
that may be inherent in the material itself; for example, in
ferromagnets.
MagnetizationMagnetization is not always uniform within a body, but
rather varies between different points.
MagnetizationMagnetization also describes
how a material responds to an applied magnetic field as well as the
way the material changes the magnetic field, and can be used to
calculate the forces that result from those interactions
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Magnetic Moment
The magnetic moment of a magnet is a quantity that determines the
torque it will experience in an external magnetic field. A loop of
electric current, a bar magnet, an electron, a molecule, and a planet
all have magnetic moments.
The magnetic moment may be considered to be a vector having a
magnitude and direction. The direction of the magnetic moment points
from the south to north pole of the magnet (inside the magnet). The
magnetic field produced by the magnet is proportional to its magnetic
moment. More precisely, the term magnetic moment normally refers to a
system's magnetic dipole moment, which produces the first term in the
multipole expansion of a general magnetic field
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Triboelectric Effect
The triboelectric effect (also known as triboelectric charging) is a
type of contact electrification on which certain materials become
electrically charged after they come into frictional contact with a
different material.[citation needed] Rubbing glass with fur, or a
plastic comb through the hair, can build up triboelectricity. Most
everyday static electricity is triboelectric. The polarity and
strength of the charges produced differ according to the materials,
surface roughness, temperature, strain, and other properties.
The triboelectric effect is not very predictable, and only broad
generalizations can be made. Amber, for example, can acquire an
electric charge by contact and separation (or friction) with a
material like wool. This property was first recorded by
ThalesThales of
Miletus. The word "electricity" is derived from William Gilbert's
initial coinage, "electra", which originates in the Greek word for
amber, ēlektron
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